Two years ago, mammalian target of rapamycin or mTOR, a signaling protein, was identified as a key mediator of the antidepressant effects of ketamine, the first rapidly acting antidepressant medication to be identified. Several years later, a group at the National Institutes of Mental Health Intramural Program reported that scopolamine, a muscarinic acetylcholine receptor antagonist, also produced rapidly appearing antidepressant effects, similar to the actions of ketamine.